1. Field of the Invention
The present invention relates to a display panel such as a liquid crystal display panel used in television sets, personal computers, word processors, OA (Office Automation) apparatuses, or the like.
2. Description of the Related Art
Such a liquid crystal display panel has a structure where a pair of substrates are provided so as to oppose each other with a liquid crystal layer being interposed therebetween as a display medium. One of the pair of substrates is an active matrix substrate, in which a plurality of signal lines and a plurality of scanning lines are provided so as to cross each other via an insulation film. A pixel electrode is provided in the vicinity of an intersection between the signal line and the scanning line and is connected to the signal lines and the scanning lines via a TFT (Thin Film Transistor) as a switching element. Each of the pixel electrodes is provided with a signal from the corresponding signal line via the TFT, which is switched by a signal from the corresponding scanning line. Thus, a voltage is applied to the liquid crystal layer between the pixel electrode and an opposing counter electrode, thereby changing the optical characteristics of the corresponding portion of the liquid crystal layer between the electrodes. This change in the optical characteristics is visually perceived as a display pattern.
When a voltage of, for example, about 100 V or more generated by an electrostatic charge, or the like, is applied to the signal line or the scanning line, the characteristics of the TFT may deteriorate, or the insulation film between the signal line and the scanning line may be broken. In such a case, a linear defect or a display non-uniformity may appear in a displayed image, thus lowering the display quality. Since an electrostatic charge of such a magnitude often occurs during a step of producing the active matrix substrate or a step of rubbing an alignment film for aligning the liquid crystal layer, it is impossible to completely avoid such problems as described above.
In view of this, an active matrix substrate provided with a short-circuiting line, as shown in FIGS. 7 and 8, has been conventionally used.
FIG. 7 shows an equivalent circuit of such a conventional active matrix substrate 101. The active matrix substrate 101 includes a transmissive substrate 1 made of a glass plate, or the like, as well as a plurality of signal lines 2 and a plurality of scanning lines 3 provided to cross each other via an insulation film. The active matrix substrate 101 further includes TFTs 4 in the vicinity of the intersection between the signal lines 2 and the scanning lines 3 as switching elements, and pixel electrodes 5. A display region is defined by the plurality of pixel electrodes 5 arranged in a matrix. Each of the pixel electrodes 5 is connected to a corresponding TFT 4. The signal lines 2 and the scanning lines 3 extend beyond the display region. A signal input terminal 6 is provided at one end of each signal line 2 while a signal input terminal 7 is provided at one end of each scanning line 3. Furthermore, a short-circuiting line 8 is formed around the display region. Until a certain point in the production process, the short-circuiting line 8 is connected to both ends of the signal lines 2 and the scanning lines 3.
FIG. 8 is a plan view illustrating another conventional active matrix substrate 111. Elements in FIG. 8 which are functionally the same as those in FIG. 7 are denoted by the same reference numerals and will not be further described. In FIG. 8, for simplicity, elements provided inside a display region 20 and some of the lines and terminals provided around the display region 20 are not shown. In this active matrix substrate, the short-circuiting line 8 is connected to one end of each signal line 2 at which the signal input terminal 6 is not provided and to one end of each scanning line 3 at which the signal input terminal 7 is not provided.
Such an active matrix substrate is attached to a counter substrate having a transmissive substrate and counter electrodes provided thereon. Then, a liquid crystal material is injected between the substrates, thereby completing the liquid crystal display panel. Herein, the panel cannot be driven with the signal lines 2 and the scanning lines 3 being short-circuited by the short-circuiting line 8. Therefore, the short circuit is removed before the liquid crystal panel is completed by severing the substrate 111 along a severance line 10.
As described above, the short-circuiting line 8 is provided to connect the signal lines 2 and the scanning lines 3 to one another, whereby the signal lines 2 and the scanning lines 3 are always kept at the same potential. Thus, it is possible to prevent the deterioration of the TFT characteristics and the insulation breakdown between the signal lines 2 and the scanning lines 3, even if an electrostatic charge is applied during a step of producing the liquid crystal display panel.
However, in the structures illustrated in FIGS. 7 and 8, the signal lines 2 and the scanning lines 3 are electrically isolated from one another after the active matrix substrate is severed. Thus, it is not possible to prevent the deterioration of the TFT characteristics and the insulation breakdown between the signal lines 2 and the scanning lines 3 due to an electrostatic charge generated during steps after the severance step. Moreover, even after the liquid crystal display panel is completed, the TFT, whose characteristics can deteriorate even by an applied voltage of about 100 V, is always subject to an influence of an electrostatic charge until it is incorporated in a shield case. For example, the TFT is subject to the influence of an electrostatic charge during steps of connecting drivers to the panel, attaching a polarizer thereto, and incorporating the panel into a shield case. Thus, it is very difficult in practice to completely prevent an electrostatic charge of such a magnitude from being generated and influencing the TFTs.
Furthermore, in the structure illustrated in FIG. 7, after the severance, each edge of the substrate 101 includes severed sections of the signal lines 2 or the scanning lines 3. In the structure illustrated in FIG. 8, two edges of the counter substrate (e.g., the upper and left edges, as in FIG. 8), along which the signal input terminals 6 or 7 are not provided, will have severed sections of either the signal lines 2 or the signal lines 3 after the severance. An electrostatic charge entering the panel through these severed sections often causes a problem, thereby significantly lowering the product yield.
Moreover, in the structures illustrated in FIGS. 7 and 8, until the active matrix substrate is severed and the short circuit by the short-circuiting line 8 is removed, all the signal lines 2 and the scanning lines 3 are short-circuited, whereby it is not possible to conduct a test for detecting a short circuit between the signal lines 2 and the scanning lines 3 or for detecting a disconnection of the lines.
In view of this, another type of conventional active matrix substrate 121 is known, which includes elements 12 and inner short-circuiting line 13, as shown in FIG. 9.
FIG. 9 shows an equivalent circuit of such a conventional active matrix substrate 121. Elements in FIG. 9 which are functionally the same as those in FIG. 7 are denoted by the same reference numerals and will not be further described. In this active matrix substrate 121, the inner short-circuiting line 13 is separately provided inside the short-circuiting line 8, where the signal lines 2 and the scanning lines 3 are connected to the inner short-circuiting line 13 via the elements 12. As the element 12, a high resistance element made of a semiconductor thin film, or the like, or a non-linear element which exhibits non-linear resistance values for different applied voltages may be used.
In this structure, even after the active matrix substrate 121 is severed along the severance line 10 so as to disconnect the signal lines 2 and the scanning lines 3 from the short-circuiting line 8, there still remain connections of the signal lines 2 and the scanning lines 3 with the inner short-circuiting line 13. Thus, even when an electrostatic charge is applied during steps after the substrate is severed, the electric charge is dispersed to all of the signal lines 2 and the scanning lines 3 via the elements 12 and the inner short-circuiting line 13. Thus, it is possible to prevent the deterioration of the TFT characteristics and the insulation breakdown between the signal lines 2 and the scanning lines 3. Herein, the connection resistance between the signal lines 2 and the inner short-circuiting line 13, and between the scanning lines 3 and the inner short-circuiting line 13, is set to a value which is sufficiently high to eliminate problems in conducting a test for detecting a short circuit between the signal lines 2 and the scanning lines 3, for detecting a disconnection of the lines during the production process of the liquid crystal display panel, or in actually driving the completed liquid crystal display panel.
In the conventional examples illustrated in FIGS. 7 and 8, after the active matrix substrate is severed and the short circuit between the signal and scanning lines 2 and 3 and the short-circuiting line 8 is removed, each of the signal lines 2 and the scanning lines 3 is electrically isolated from one another. Therefore, when an electrostatic charge is applied after the substrate is severed, it is not possible to prevent the deterioration of the switching element characteristics and the insulation breakdown between the signal lines 2 and the scanning lines 3. Moreover, as the substrate edges have severed sections of the signal lines 2 or the scanning lines 3, an electrostatic charge entering the panel through these severed sections often causes a problem. Furthermore, until the active matrix substrate is severed and the short circuit by the short-circuiting line 8 is removed, all the signal lines 2 and the scanning lines 3 are electrically connected to each other, whereby it is not possible to conduct a test for detecting a short circuit between the signal lines 2 and the scanning lines 3 nor detect a disconnection of the lines.
In the conventional example illustrated in FIG. 9, the elements 12 may be broken or the characteristics thereof may deteriorate due to an applied electrostatic charge, so that leakage might occur between the signal lines 2 and the scanning lines 3, or non-uniformity may occur in the connection resistance between the lines and the inner short-circuiting line 13, thus lowering the display quality. Moreover, the resistance of the elements 12 is set to a value which is sufficiently high to eliminate problems in actually driving the display panel. Normally, the resistance value of the elements 12 is set to be higher than the resistance value of the signal lines 2 and the scanning lines 3 by an order of magnitude or more. Therefore, when an electrostatic charge is applied through the severed edge (such as C in FIG. 9), most of the electric charge flows to the signal lines 2 or the scanning lines 3 due to the resistance difference. Thus, substantially no electric charge is dispersed to the inner short-circuiting line 13 via the elements 12, whereby the characteristics of the TFTs 4 connected to the signal lines 2 or the scanning lines 3 may deteriorate, or the insulation between the lines may be broken.
According to one aspect of this invention, a display panel includes: a first substrate and a second substrate opposing each other with a display medium interposed therebetween; a plurality of signal lines and a plurality of scanning lines provided on the first substrate to cross each other and be insulated from each other; and a plurality of pixel electrodes each provided in a vicinity of an intersection between one of the plurality of signal lines and one of the plurality of scanning lines so as to be connected to the one of the plurality of signal lines and the one of the plurality of scanning lines via a switching element, while the plurality of pixel electrodes define a display region of the display panel. At least one of each of the plurality of signal lines and each of the plurality of scanning lines has a high resistance portion proximate an end thereof outside the display region. The high resistance portion is interposed at least partially between the first substrate and the second substrate.
In one embodiment of the invention, the high resistance portion is formed of a material including semiconductor, a metal, and a metal oxide.
In another embodiment of the invention, the high resistance portion is formed of a film having a specific resistance higher than a specific resistance of a film which forms portions of the plurality of signal lines and the plurality of the scanning lines in the display region.
According to another aspect of this invention, a display panel includes: a first substrate and a second substrate opposing each other with a display medium interposed therebetween; a plurality of signal lines and a plurality of scanning lines provided on the first substrate to cross each other and be insulated from each other; and a plurality of pixel electrodes each provided in a vicinity of an intersection between one of the plurality of signal lines and one of the plurality of scanning lines so as to be connected to the one of the plurality of signal lines and the one of the plurality of scanning lines via a switching element, while the pixel electrodes define a display region of the display panel. A first electrode, for inducing an electrostatic charge applied to the display panel to the first electrode, is provided outside the display region in a vicinity of an end of at least one of each of the plurality of signal lines and each of the plurality of scanning lines, the first electrode being insulated from the plurality of signal lines and the plurality of scanning lines.
In one embodiment of the invention, the first electrode is electrically connected to a counter electrode on the second substrate.
In another embodiment of the invention, the first electrode is superimposed on, and insulated from, the plurality of signal lines and the plurality of scanning lines.
In still another embodiment of the invention, the first electrode is interposed between, and insulated from, two adjacent ones of the plurality of signal lines and the plurality of scanning lines.
In still another embodiment of the invention, the first electrode is wider or larger in area than the portion of the plurality of signal lines and the plurality of scanning lines near an edge of the first substrate.
Hereinafter, the effect of the present invention will be described.
In the present invention, the signal line and/or the scanning line has a high resistance portion proximate the end thereof outside the display region. Since the signal lines and the scanning lines are connected to the short-circuiting line via the high resistance portions, even if an electrostatic charge is applied before the substrate is severed, the electrostatic charge can be dispersed to the other lines via the high resistance portion and the short-circuiting line, whereby the deterioration of the switching element characteristics and the insulation breakdown between the lines will not occur due to an electrostatic charge. Moreover, since the resistance value of the high resistance portion is sufficiently higher than the resistance value of the signal line or the scanning line, it is possible to conduct a test for detecting a disconnection of the signal lines and the scanning lines or for detecting a leakage between these lines, with the connection of these lines to the short-circuiting line still intact.
Moreover, the high resistance portion is protruding from, or interior to, an edge of the counter substrate, whereby when the substrate is severed, part or all of the high resistance portion remains between the severed edge of the substrate and the display region. Thus, even when a static electric charge is applied during steps after the substrate is severed, the voltage of the applied electrostatic charge is lowered by the high resistance portion before it reaches the display region, whereby the deterioration of the switching element characteristics and the insulation breakdown between the lines will not occur. Furthermore, since the high resistance portion is located closer to the substrate edge than the signal input terminals, the high resistance portion does not influence a signal applied to the signal input terminals for actually driving the display panel, even with the high resistance portion remaining on the substrate after the display panel is completed.
It is preferable that the high resistance portion is made of a film having a specific resistance higher than a specific resistance of a film which forms portions of the signal lines and the scanning lines excluding the high resistance portion. Any film such as a semiconductor film, a metal film or a metal oxide film may be used for this purpose. Particularly, it is preferable that the high resistance portion is formed of a material which forms the active matrix substrate, whereby no additional production step is required.
According to an alternative example of the present invention, a discharge-inducing electrode is provided outside the display region in the vicinity of the end of either or both of the signal line and the scanning line so as to be insulated from these lines. Therefore, even when an electrostatic charge is generated around the display panel during a step of producing the display panel or after the display panel is completed, the electrostatic charge is discharged to the discharge-inducing electrode, whereby the application of the electrostatic charge to the signal lines and the scanning lines is suppressed. Thus, the deterioration of the switching element characteristics and the insulation breakdown between the lines will not occur.
When the discharge-inducing electrode is connected to the counter electrode, the applied electrostatic charge is dispersed to the entire display panel, whereby it is possible to avoid the influence of the electrostatic charge.
The discharge-inducing electrode may be superimposed on, and insulated from, the scanning lines and the signal lines, or it may be interposed between, and insulated from, two adjacent signal lines or two adjacent scanning lines. The discharge-inducing electrode may further be provided outside the outermost lines so as to be insulated from the outermost lines. In any case, since the discharge-inducing electrode is electrically insulated from the lines, the electrostatic charge applied to the discharge-inducing electrode will not be applied to the scanning lines or the signal lines.
The discharge-inducing electrode is preferably wider or larger in area than the scanning lines or the signal lines at the edge of the substrate, so that the electrostatic charge applied around the display panel is more easily induced to the discharge-inducing electrode.
Thus, the invention described herein has the advantage of providing a display panel in which it is possible to prevent the deterioration of the switching element characteristics and the insulation breakdown between the lines due to an electrostatic charge even after the substrate is severed.
This and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.